This invention relates to a heat treatment method for metals, more particularly a heat treatment method for carburizing steels in a continuous type atmosphere heat treatment furnace.
As described in Japanese Post-Examination Publication No. 58-27323 for example,it has been known that an exhaust gas from a combustion heating circuit in a furnace is generated to an exothermic gas which is, in turn, utilized as a furnace atmosphere gas. More particularly, this kind of atmosphere gas is made by freezing and dehydrating the exothermic generated gas. The gas thus converted is generally consisted of N.sub.2 (65-88%), CO(0-13%), CO.sub.2 (7-13%), H.sub.2 (0-17%) and H.sub.2 O(0-3%). While this gas is reductive against iron, steel and so on, it can not be utilized for carburizing steels.